1. Field of the Invention
The present invention is directed to the field of thermal compensators that provide linear movement in response to changes in thermal temperatures and more specifically to the area of thermal compensators that utilize a liquid as the thermal responsive medium.
2. Description of the Prior Art
The problem of focus distortion in optical systems due to changes in temperature has been frequently discussed in the prior art. Generally, ambient temperature variations cause glass lenses to expand or to contract and vary the indices thereof. The lens mounts also tend to expand or contract due to changes in temperature and therefore additionally distort the focal characteristics of the optical system. In order to maintain a fixed focal point throughout wide variations in temperature, many passive systems have been developed for compensating the above-mentioned expansion and contraction. The prior art with respect to passive compensator systems falls into two major groups, which include bi-metal mechanisms, such as shown in U.S. Pat. No. 4,190,325 and U.S. Pat. No. 4,236,790; and liquid expansion structures, such as disclosed in U.S. Pat. Nos. 3,503,004 and 3,612,664.
In general, applicant has found the liquid thermal compensators to be favored over the bi-metal types due to the difficulty in repeatedly obtaining metals that have precise values of thermal coefficient; and since the relatively small coefficients of expansion require a relatively long length of metal to achieve significant compensation. Even though the prior art liquid compensator devices overcome the problems found in bi-metal type devices, the prior art fails to suggest how either type of passive mechanism may be accurately tuned to provide a desired amount of compensation over a range of temperatures after they are constructed.